Non-contacting sensors are well known. Such sensors are particularly useful when the constant moving, frictional contact between parts in a contacting sensor which might otherwise be used causes excessive wear of the parts and ultimate failure of the sensor. Non-contacting sensors are required in those applications where the parts move, relative to one another, in such a way that connections cannot be maintained. For example, a rotating shaft, undergoing a number of rotations, will cause the connecting wires of a contacting sensor to twist and break as the shaft turns.
Inductance coils are commonly used in noncontacting sensors. Typically, such sensors include a pair of coils which are inductively coupled. As one coil moves relative to the other, or as a "spoiler" moves between the two coils, the inductive coupling between the two coils changes in accordance with the relative movement of the coils or the movement of the "spoiler".
One technique for processing the signals of an inductance coil sensor to develop an indication of changes in the parameter being monitored involves measuring the effect of a shift in resonance frequency of a tank circuit which includes, as one of its components, one of the inductance coils. As one coil moves relative to the other, or as a "spoiler" moves between the two coils, the resonance frequency of the tank circuit shifts in accordance with the movement.
Three copending applications, filed in the name of the present applicant and assigned to the same assignee to which this application is assigned, are directed to non-contacting inductance coil sensors and processing circuitry which detects shifts in the characteristics of a tank circuit as the inductive coupling between two coils is altered by changes in the parameter being monitored. These copending applications, all filed on Feb. 11, 1985, are "Inductance Coil Sensor", Ser. No. 700,295; "Sensor Apparatus", Ser. No. 700,081; and "Sensor Apparatus", Ser. No. 700,188.
Non-contacting sensor systems, prior to those disclosed and claimed in the above-identified copending applications, have failed to satisfy concurrently the requirements of accuracy, efficient signal processing, reasonable cost, and limited size and weight. These criteria are particularly important when the sensor system is to be applied to a consumer product, such as an automobile.
The invention disclosed and claimed in the present application, employing certain of the concepts and techniques disclosed and claimed in the above-identified copending applications, extends the utility of monitoring a parameter by sensing shifts in the characteristics of a tank circuit to uses in which the sensors sense relative movements within a moving assembly. A typical use, and one which will be described in detail in this application, is sensing the twist imparted to a torqued rotating shaft.